Fast lock-in amplifier electrochemical impedance spectroscopy for big capacity lead-acid battery

Big capacity (>4000 Ah) lead acid battery is necessary to important emergency power system. Electrochemical impedance spectroscopy (EIS) of the battery is weak. Low frequency Digital Lock-in Amplifier (DLA) needs long-term sampling. Fast Fourier Transformation (FFT) needs whole number periods sampling. This paper suggests a Fast Lock-in Amplifier (FLA). It takes place of low pass filter with linear average definite digital Integrator. The FLA can output at short-term and partial period sampling. Its result is a fast linear interpolation of FFT. Results of FLA and FFT are identical at whole number periods sampling. The proposed method is verified by Valve-Regulated Lead-Acid (VRLA) battery (4200 Ah) aging tests. Microcontroller runs the proposed algorithm.